Capacitor for a semiconductor device and method for forming the same

ABSTRACT

A capacitor having high capacitance using a silicon-containing conductive layer as a storage node, and a method for forming the same, are provided. The capacitor includes a storage node, an amorphous Al 2 O 3  dielectric layer, and a plate node. The amorphous Al 2 O 3  layer is formed by a method in which reactive vapor phase materials are supplied on the storage node, for example, an atomic layered deposition method. Also, the storage node is processed by rapid thermal nitridation before forming the amorphous Al 2 O 3  layer. The amorphous Al 2 O 3  layer is densified by annealing at approximately 850° C. after forming a plate node, to thereby realize the equivalent thickness of an oxide layer which approximates a theoretical value of 30 Å.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a capacitor of a semiconductordevice, and a method for forming the same.

[0003] 2. Description of the Related Art

[0004] As semiconductor devices become more highly integrated, there isa necessity for reducing the area occupied by a capacitor, which in turncauses a reduction in the capacitance. To solve this problem, thestructure of the capacitor is changed or a material having a highdielectric constant is employed. For instance, a method has beenproposed for forming a capacitor using a Ta₂O₅ dielectric layer or a(Ba,Sr)TiO₃ (BST) dielectric layer having a dielectric constant higherthan that of an oxide/nitride/oxide (ONO) layer structure typically usedfor a dynamic random access memory (DRAM).

[0005] However, the process is complicated. The structure of a typicalcapacitor is a silicon/insulator/silicon (SIS) layer structure in whichpolycrystalline silicon layers doped with an impurity are used for plateand storage nodes. However, a metal/insulator/silicon (MIS) layer or ametal/insulator/metal (MIM) layer structure is required for the case ofusing the Ta₂O₅ layer, and the MIM layer structure is required for thecase of using the BST layer. That is, the structure of the capacitormust be changed.

[0006] If the Ta₂O₅ layer is used, then in order to overcome low stepcoverage, a layer must be formed using chemical vapor deposition (CVD)at a low temperature, which is a surface kinetic regime, and which maycause a deficiency in oxygen, leaving hydrocarbon residue in the layeror deterioration in crystallization. Thus, the dielectric constant isreduced, and insulating properties are poor. Accordingly, to overcomethese problems, a dry O₂ annealing process at a high temperature isadditionally required. Also, there has been disclosed a method forcompensating for the insulating properties of the Ta₂O₅ layer by usingan oxide layer under the Ta₂O₅ layer generated by a dry annealingprocess (Y. Ohyi, “Ta₂O₅ Capacitor Dielectric Material for Giga-bitDRAMs”, IEDM Tech. Dig., 1994. p 831).

[0007] Meanwhile, diffusion is easily caused by discontinuities in theatomic arrangement at a grain boundary. Thus, when a thick oxide layeris formed to compensate for the leakage current properties of the Ta₂O₅layer, diffusion of oxygen into the grain boundary is increased, tothereby oxidize a plate node. Accordingly, a reaction preventing layeris required between the Ta₂O₅ layer and the plate node of the capacitorto prevent reaction of the Ta₂O₅ layer with the plate node (U.S. Pat.No. 4,891,684).

[0008] In order to obtain excellent leakage current properties, aSchottky barrier must be formed between a BST layer and an electrode. Inorder to form the Schottky barrier, an electrode should be formed ofmaterials having a high work function, e.g., a metal (see Soon Oh Park,“Fabrication and Electrical Characterization of Pt/(Ba, Sr)TiO₃/PtCapacitors for Ultralarge-scale Integrated Dynamic Random Access MemoryApplications”, Jpn. J. Appl. Phys. Vol. 35, 1996, pp. 1548-1552). Inorder to employ the metal electrode, an ohmic contact must be formed atan interface between the metal electrode and the polycrystalline siliconlayer doped with an impurity. That is, an intermediate layer forming theohmic contact must be formed and a barrier layer must be employed.

[0009] The material layer of a high dielectric constant, such as theTa₂O₅ layer or the BST layer, requires a complicated process andstructure, that is, a change of the structure of the capacitor to theMIM or MIS structure.

SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide a capacitorof a semiconductor device, using a silicon-containing conductive layeras a storage node to increase capacitance.

[0011] It is another object to provide a method for forming a capacitorof a semiconductor device, using a silicon-containing conductive layeras a storage node to increase capacitance. Other and further objectswill appear hereafter.

[0012] Accordingly, to achieve one objective, the capacitor of thepresent invention includes a storage node, a dielectric layer and aplate node. The storage node is a silicon-containing conductive layersuch as a polycrystalline silicon layer doped with an impurity. Also,the storage node has a three dimensional structure selected from thegroup consisting of a stack type, a hemispherical grained silicon layertype and a cylinder type.

[0013] The dielectric layer is formed of amorphous Al₂O₃, on the storagenode. Here, the amorphous Al₂O₃ layer is formed by transmitting vaporreactive materials supplied by each source to the storage node in whichreactions are sequentially processed. The thickness of the dielectriclayer is 10˜300 Å using an atomic layered deposition method, and thethickness of the amorphous Al₂O₃ dielectric layer is 40˜70 Å. Also, areaction preventing layer is formed of one selected from the groupconsisting of silicon oxide, silicon nitride and silicon oxynitridelayer.

[0014] The plate node is a conductive layer formed of polycrystallinesilicon doped with impurities. Alternatively, the plate node is aconductive layer formed of a refractory metal, a refractory metalsilicide material or a refractory metal nitride material. For example,the refractory metal may be W, Mo, Ta, Ti or Cr. Also, the refractorymetal silicide material is formed by silicidation of a refractory metalsilicide material, such as Wsi₂, MoSi₂, TaSi₂ or TiSi₂, among others.The refractory metal nitride material is formed by nitrification of arefractory metal, such as TiN.

[0015] To achieve another objective, a storage node is formed. Thestorage node is a polycrystalline silicon layer doped with an impurity,and the storage node has a three-dimensional structure selected from thegroup consisting of a stack type, a hemispherical grained silicon layertype and a cylinder type.

[0016] Then, a reaction preventing layer is formed on the storage node.The reaction preventing layer is formed by annealing the storage node at300˜1200° C. In detail, a rapid thermal nitridation (RTN) process isperformed using a N₂ source such as NH₃ gas as an ambient gas atapproximately 900° C. Thus, the reaction preventing layer of the storagenode may be formed of silicon oxide (SiO₂), silicon nitride (SiN) orsilicon oxynitride (SiON).

[0017] Next, a dielectric layer is formed of an amorphous Al₂O₃ layer onthe storage node. The amorphous Al₂O₃ layer is formed to a thickness of10-300 Å by a method of supplying a reactive vapor phase material fromeach of several sources in sequence on a layer to be reacted with, i.e.,the storage node, in which reaction, that is, deposition is performed incycles, for instance, an atomic layer deposition (ALD) method.Preferably, the amorphous Al₂O₃ layer is formed to a thickness of 40-80Å. The atomic layer deposition method is performed using one selectedfrom the group consisting of Al(CH₃)₃ and AlCl₃ as an aluminum source,and the storage node is processed by hydrogen passivation treatmentbefore performing the atomic layered deposition.

[0018] Then, a plate electrode is formed on the dielectric layer. Theplate node is a conductive layer formed of polycrystalline silicon dopedwith impurities. Alternatively, the plate node is a conductive layerformed of a refractory metal, a refractory metal silicide material or arefractory metal nitride material. For example, the refractory metal maybe W, Mo, Ta, Ti or Cr. Also, the refractory metal silicide material isformed by silicidation of a refractory metal silicide material, such asWSi₂, MoSi₂, TaSi₂ or TiSi₂, among others. The refractory metal nitridematerial is formed by nitrification of a refractory metal, such as TiN.

[0019] Also, a primary densification is performed on the amorphous Al₂O₃dielectric layer, after the step of forming a plate node, by annealingthe amorphous Al₂O₃ dielectric layer at a temperature below thetemperature of crystallizing the amorphous Al₂O₃ layer, at 150-900° C.The annealing is performed using an ambient gas selected from the groupconsisting of O₂, NO and N₂ gas, or in a vacuum. Preferably, the primarydensification is performed at 850° C.

[0020] Also, a secondary densification is additionally performed on theamorphous Al₂O₃ dielectric layer, before the step of forming a platenode, by annealing the amorphous Al₂O₃ dielectric layer at a temperaturebelow the temperature of crystallizing the amorphous Al₂O₃ layer, at150-900° C., using an ambient gas selected from the group consisting ofO₂, NO and N₂ gas, or in a vacuum. Preferably, the annealing isperformed using O₂ as an ambient gas at approximately 450° C.

[0021] Accordingly, the silicon-containing conductive layer is used asthe storage node, and the capacitance can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above objectives and advantages of the present invention willbecome more apparent by describing in detail a preferred embodimentthereof with reference to the attached drawings in which:

[0023]FIG. 1 is a sectional view of a capacitor according to anembodiment of the present invention;

[0024]FIGS. 2 through 4 are sectional views showing structures of astorage node used for a capacitor according to embodiments of thepresent invention;

[0025]FIG. 5 is a sectional view for illustrating the step of formingthe storage node on a semiconductor substrate;

[0026]FIG. 6 is a sectional view for illustrating the step of forming adielectric layer on the storage node of FIG. 5;

[0027]FIG. 7 is a graph showing the relationship between the thicknessof an equivalent oxide layer of an amorphous Al₂O₃ and applied drivingvoltage;

[0028]FIG. 8 is a graph showing leakage current density with respect toa drive voltage applied to a capacitor having an amorphous Al₂O₃ layerof 60 Å; and

[0029]FIG. 9 is a graph showing electrical characteristics of acapacitor according to various condition variables during annealing atapproximately 450° C. after forming an amorphous Al₂O₃ layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The present invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the thickness of layers and regionsare exaggerated for clarity. Like numbers refer to like elementsthroughout. It will also be understood that when a layer is referred toas being “on” another layer or substrate, it can be directly on theother layer or substrate, or intervening layers may also be present.

[0031] Referring to FIG. 1, a capacitor according to an embodiment ofthe present invention includes a storage node 200, a dielectric layer400 and a plate node 500. The storage node 200 is electrically connectedto an active region of a semiconductor substrate 100 through a contacthole formed in an interlevel insulating layer 150 covering thesemiconductor substrate 100. A silicon-containing conductive layer suchas a polycrystalline silicon layer doped with an impurity is used forthe storage node 200.

[0032] An amorphous aluminum oxide Al₂O₃ layer is used for thedielectric layer 400 covering the storage node 200. The Al₂O₃ layer haslittle difference in dielectric constant between its crystalline phase,such as α-Al₂O₃ and γ-Al₂O₃, and its amorphous phase, and has adielectric constant of about 10. However, the amorphous Al₂O₃ layer ismore easily oxidized than silicon oxide, has a low permeability ofalkali ions and excellent properties. Also, the amorphous Al₂O₃ layerhas a smooth morphology and high resistance to diffusion through a grainboundary, and thus diffusion of oxygen through it can be suppressed.

[0033] The amorphous Al₂O₃ layer is formed by sequentially supplying areactive vapor phase material from each of several sources on a layer,i.e., the storage node. Particularly, a whole amorphous Al₂O₃ layer isobtained by repeating the formation of thin films. For example, anatomic layer deposition (ALD) method may be used.

[0034] By forming the amorphous Al₂O₃ layer using the ALD method,supplying in sequence the reactive vapor phase materials on a layerwhere reaction for forming the Al₂O₃ layer is performed, high conformitymay be obtained and a step coverage may reach about 100%. Few impuritiesremain in the amorphous Al₂O₃ layer due to process properties of the ALDmethod. It has been known that an Al₂O₃ layer formed by sputtering haspoor step coverage and if the Al₂O₃ layer is formed by CVD, it isdifficult to remove remaining impurities and form a thin layer.Accordingly, in a preferred embodiment, the amorphous Al₂O₃ layer isformed by the ALD method, and thus has high step coverage and a moreamorphous state. The amorphous Al₂O₃ layer is formed to a thickness of10-300 Å, preferably 40-80 Å.

[0035] Also, a reaction preventing layer 300 of silicon oxide (SiO₂),silicon nitride (SiN) or silicon oxynitride (SiON) may be further formedbetween the storage node 200 and the dielectric layer 400. However,since the amorphous Al₂O₃ layer has low diffusivity of oxygen, thereaction preventing layer 300 can be omitted. The plate node 500 formedon the dielectric layer 400 is formed of a conductive layer formed of apolycrystalline silicon doped with impurities. Alternatively, the plate500 is formed of a conductive layer formed of a refractory metal, arefractory metal suicide material or a refractory metal nitridematerial. For example, the refractory metal may be W, Mo, Ta, Ti or Cr.Also, the refractory metal silicide material is formed by silicidationof a refractory metal silicide material, such as WSi₂, MoSi₂, TaSi₂ orTiSi₂, among others. The refractory metal nitride material is formed bynitrification of a refractory metal, such as TiN.

[0036] Meanwhile, the structures of a storage node of the capacitor maybe formed in a variety of three-dimension structures. For instance, astack type storage node 200 as shown in FIG. 1, can be adopted to thecapacitor structure. Alternatively, a hemispherical grained silicon(HGS) layer may be formed on a surface of an electrode as shown in FIG.2, so that the storage node 200 a has the HGS structure, which increasesthe surface area due to its irregularity. Other structures may be used,such as a cylinder type storage electrode 200 b as shown in FIG. 3, or astorage node 200 c as shown in FIG. 4 in which the hemispherical grainedsilicon layer is formed on the surface of the cylinder type electrode toincrease the surface area. Even though three-dimensional storage nodessuch as 200, 200 a, 200 b and 200 c are employed, a high conformity canbe realized in the amorphous Al₂O₃ layer when the amorphous Al₂O₃ isformed by the ALD process. The high conformity avoids problems such aspoor step coverage. Although preferred embodiment storage nodes 200, 200a, 200 b and 200 c are illustrated, other structures are possible aswould be well known to one skilled in the art.

[0037] Referring to FIG. 5, a storage node 200 is formed on asemiconductor substrate 100 where an interlevel insulating layer 150 isformed. The storage node 200 in the present embodiment may be shaped ina three-dimensional form such as a hemispherical grained silicon layertype or a cylinder type as described with respect to FIGS. 2 through 4,instead of the stack type. Also, the storage node 200 is formed of aconductive layer of a silicon group, such as a polycrystalline siliconlayer doped with an impurity.

[0038] Then, the storage node 200 may be annealed by a rapid thermalprocess (RTP), to thereby additionally form a reaction preventing layer300 covering the storage electrode 200. The annealing is performed at300-1200° C., preferably 900° C., using an NH₃ gas as a nitrogen sourcefor 60 sec, i.e., through rapid thermal nitridation (RTN). Through theannealing, the silicon of the storage node 200 reacts with nitrogen, tothereby form a SiN layer used as a reaction preventing layer 300. Also,a silicon oxide or silicon oxynitride layer may be used instead of thesilicon nitride layer for the reaction preventing layer 300.

[0039] The reaction preventing layer 300 more completely prevents oxygenfrom being diffused into the storage node 200 during the annealingprocess, which is performed later, using an ambient gas of oxygen. Thatis, the equivalent thickness (ET) of an oxide layer can be preventedfrom increasing due to diffusion of oxygen. However the silicon nitridelayer need not be formed by the RTP. This is because low oxygendiffusivity is maintained by the Al₂O₃ layer.

[0040] Referring to FIG. 6, a native oxide layer remaining on thestorage node 200 is completely removed through hydrogen passivationtreatment.

[0041] Then, the amorphous Al₂O₃ layer is formed on the storage node 200by a method in which each reactive vapor phase material from severalsources is supplied step by step onto the storage node 200. This may beachieved in various ways, particularly by the ALD method. By the ALDmethod, an aluminum (Al) layer is formed on the storage node 200 usingan aluminum source, to a degree of atomic sized thickness. Then, the Allayer is oxidized with an oxidation agent to form an Al₂O₃ layer havingan atomic-sized thickness, i.e., approximately 0.5-50 Å. Subsequently,the step of forming the Al₂O₃ layer having an atomic-sized thickness isperformed in cycles, to thereby form an amorphous Al₂O₃ layer of 10-300Å. Preferably, the amorphous Al₂O₃ layer is formed to a thickness of40-80 Å.

[0042] Specifically, Al(CH₃)₃ or AlCl₃, preferably Al(CH₃)₃ is used asan aluminum source. Preferably, vaporized H₂O is used as the oxidationagent. When the step of oxidizing the Al layer using the oxidation agentis performed, the temperature of the semiconductor substrate 100 is150-400° C., preferably approximately 350° C. Also, the amorphous Al₂O₃layer is grown to a thickness of approximately 2 Å by each cycle. Theamorphous phase of the amorphous Al₂O₃ layer is realized according tocharacteristics of the ALD process. Also, the Al₂O₃ layer has highconformity according to the characteristics of the ALD. Thus, a stepcoverage of approximately 100% can be realized.

[0043] Then, a plate electrode 500 as shown in FIG. 1 is formed on thedielectric layer 400. The plate electrode 500 is formed of a conductivelayer formed of a polycrystalline silicon doped with impurities.Alternatively, the plate electrode 500 is formed of a conductive layerformed of a refractory metal, a refractory metal silicide material or arefractory metal nitride material. For example, the refractory metal mayby W, Mo, Ta, Ti or Cr. Also, the refractory metal silicide material isformed by silicidation of a refractory metal silicide material, such asWSi₂, MoSi₂, TaSi₂ or TiSi₂, among others. The refractory metal nitridematerial is formed by nitrification of a refractory metal, such as TiN.

[0044] The grown amorphous Al₂O₃ layer has a refractivity ofapproximately 1.64λ, where λ=633.0 nm. The amorphous Al₂O₃ layer can bedensified through a subsequent annealing process. The degree ofdensification can be evaluated by measuring the refractivity and thethickness of the layer. That is, the amorphous Al₂O₃ layer is grown, andthen annealed under an O₂ ambient gas, after that the refractivity ofthe annealed Al₂O₃ layer is measured to estimate the degree of thedensification. TABLE 1 Characteristics before and after growing Al₂O₃layer Refractivity (λ = 633.0 nm) Aftergrowing 1.64 After annealing1.692 (about 800° C., O₂, for 30 min)

[0045] As shown in Table 1, the refractivity of the amorphous Al₂O₃layer is increased, through O₂ annealing, which leads to densificationof the amorphous Al₂O₃ layer. Thus, the dielectric constant of theamorphous Al₂O₃ layer is increased, so that the equivalent thickness(ET) of an oxide is minimized.

[0046] To show how the amorphous Al₂O₃ layer suppresses O₂ diffusion,thickness of the SiO₂ layer formed on a bare wafer was measured as afunction of the thickness of a layer of Al₂O₃ formed on the wafer. Thatis, an amorphous Al₂O₃ layer having various thicknesses was formed on abare wafer. The wafer was treated with standard cleaners I and HF, andthen the amorphous Al₂O₃ layer was annealed under an O₂ ambient gas atapproximately 800° C. Then, the thickness of the formed SiO₂ layer wasmeasured using a spectroscopic elipsometer. The results are shown inTable 2.

[0047] As shown in Table 2, if the amorphous Al₂O₃ layer is not formed,the SiO₂ layer is grown to approximately 66.6 Å. If an amorphous Al₂O₃layer is employed, the thickness of the SiO₂ layer is abruptly reduced.If the amorphous Al₂O₃ layer of approximately 100 Å is employed, theSiO₂ layer is reduced to a thickness of approximately 2 Å. As describedabove, the amorphous Al₂O₃ layer of the present embodiment suppresses O₂diffusion, so that excellent capacitor properties can be realized evenwithout the reaction preventing layer 300 being formed through the RTP.However, the reaction preventing layer 300 may be employed to completelyprevent O₂ diffusion during a subsequent process of annealing. TABLE 2Thickness of SiO₂ layer -vs- thickness of Al₂O₃ layer Thickness of Al₂O₃after annealing (Å) Thickness of SiO₂ (Å) 0 66.576 28.860 17.032 33.36918.959 48.484 11.222 82.283 3.406 98.711 2.002 258.749 1.542

[0048] In order to increase the dielectric constant, a primarydensification is performed on the amorphous Al₂O₃ layer, throughannealing. This annealing for densification can be performed at any timeafter forming the amorphous Al₂O₃ layer, preferably after forming theplate node 500. The annealing is performed at approximately 150-900° C.,preferably 850° C., which is lower than the crystallization temperatureof the amorphous Al₂O₃ layer, using O₂ gas, NO gas or N₂ gas as anambient gas, or in a vacuum. Preferably, the annealing is performed inthe ambient gas of N₂ for approximately 30 min.

[0049] The amorphous Al₂O₃ layer gives an ET value which approximates,for instance, a theoretical ET value of about 26 Å, when the thicknessof the amorphous Al₂O₃ layer is about 60 Å, and the dielectric constantof the Al₂O₃ is assumed to be 9. However, the annealing can be furtherperformed to realize a value even more closely approximating thetheoretical ET value. That is, a secondary densification is performedthrough annealing immediately after forming the amorphous Al₂O₃ layer,and this is a pretreatment for the primary densification.

[0050] Here, the secondary densification is performed at 150-900° C.,preferably 450° C., which is lower than the crystallization temperatureof the amorphous Al₂O₃ layer, using O₂ gas, NO gas or N₂ gas as anambient gas, or in a vacuum. Preferably, the secondary densification isperformed by annealing in the ambient gas of O₂ for about 30 min.

[0051] Table 3 shows various electric characteristics measured undervarious conditions in order to illustrate the effect of the secondarydensification. That is, the storage node 200 is formed from apolycrystalline silicon layer on a semiconductor substrate 100, theamorphous Al₂O₃ layer is formed, and electrical properties of thecapacitor are measured. Table 3 contains the results of tenmeasurements, showing the effects when the RTN process of NH₃ isperformed at 900° C. for 60 sec or not performed, the amorphous Al₂O₃layer is formed to 60 Å or 300 Å, and the secondary densification isperformed using O₂ at approximately 450° C. for 30 min, at approximately800° C. for 30 min, or not performed.

[0052] As shown in Table 3, the Al₂O₃ layer of about 300 Å has a leakagecurrent density of 20 nA/cm² or less, regardless of other conditions.

[0053] However, the leakage current of the Al₂O₃ layer of about 60 Å ischanged by other conditions. For example, in the case No. 7 of the Al₂O₃layer of 60 Å without RTN, and with the secondary densification at 800°C., the ET is approximately 57 Å, which is the greatest for all caseswhere the thickness of the Al₂O₃ layer is 60 Å. Also, for example, incase No. 1 with the RTN process, the ET is approximately 47 Å, which ismore than the theoretical ET value 30 Å (i.e., an RTN layer of 4 Å+anAl₂O₃ layer of 26 Å). This means that the equivalent oxide layer hasgrown.

[0054] Moreover, in case No. 3 when the Al₂O₃ layer of 60 Å thick, thetemperature of the secondary densification is 450° C., and the RTN isperformed, the ET is 40 Å, and in the case No. 6 when the Al₂O₃ layer is60 Å thick, the secondary densification temperature is 450° C. and theRTN process is not performed, the ET is 37 Å. However, in the case No.6, the leakage current density of approximately 700 nA/cm² is higher incomparison to approximately 45 nA/cm² in the case No. 3.

[0055] From these results, we note that the electric characteristics ofa capacitor are excellent in the case of performing secondarydensification at 450° C. as, for example, in case No. 3. Also, if thereaction preventing layer 300 such as a SiN₂ layer, a SiO₂ layer or aSiON layer is formed through annealing such as RTN, between the storagenode 200 and the dielectric layer 400, the electrical characteristics ofthe capacitor are enhanced. TABLE 3 Electric characteristics ofcapacitor as a function of secondary densification Thickness ThicknessTempera- leakage of of ture of O₂ Capacitance current equivalentC_(min)/ Al₂O₃ secondary (pF) density oxide layer C_(max) No. RTN layer(Å) densification C_(min) C_(max) tan δ (nA/cm²) (ET)(Å) (%) 1 yes 60800 615 661 0.012 25.8 47 93 2 300 800 235 247 0.031 ≦20 125 95 3 60 450718 772 0.009 45.77 40 93 4 300 450 259 263 0.042 ≦20 117 98 5 300 — 218229 0.045 ≦20 135 95 6 no 60 450 766 832 0.06 704.38 37 92 7 60 800 535546 0.014 37.32 57 98 8 300 450 248 252 0.019 ≦20 117 98 9 300 — 210 2190.052 ≦20 141 96 10 300 800 222 223 0.046 ≦20 138 99

[0056] As described above, when the amorphous Al₂O₃ layer is employed asthe dielectric layer 400 and the secondary densification is performed,the electrical characteristics of the capacitor are enhanced. However,the ET values realized under the above conditions do not reach thetheoretical value of 30 Å. Thus, the effect of performing the primarydensification after forming the plate node 500 will be described. Thatis, the plate node 500 is formed under conditions as shown in Table 3and then annealed at approximately 850° C. for 30 min using an ambientgas of N₂, for a primary densification, and then the electricalcharacteristics of the capacitor are measured for the ten differentprocess conditions of Table 3.

[0057] Table 4 shows the results of these measurements. In Table 4, ‘C’,‘B’, ‘T’, ‘L’ and ‘R’ indicate center, bottom, top, left and rightportions of a wafer, respectively. The primary densification can reducethe ET values for all cases as shown in Table 4. In the case that theAl₂O₃ layer is annealed at approximately 450° C. during the secondarydensification process and RTN is performed (No. 3-C), the ET value is 35Å. In the case where the other conditions are the same as that of No.3-C, but the RTN process is not performed (No. 6-C), the ET value is 31Å. Both results approximate to the theoretical value of 30 Å. Thus,these results show that the secondary densification of the amorphousAl₂O₃ layer further increases capacitance. TABLE 4 Electricalcharacteristics of capacitor depending on primary densification Tempera-Thickness Postion Thickness ture of O₂ Leakage of C_(min)/ of ofsecondary Capacitance current Equivalent C_(max) semiconductor Al₂O₃densification (pF) density oxide layer (%; ± No. RTN substrate layer (Å)(° C.) C_(min) C_(max) tan δ (nA/cm²) (ET; Å) 2V) 1 yes C 60 800 680 6900.012 7.96 44.8 98.6 2 C 300 800 250 270 0.019 15.2 118.3 92.6 3 T 60450 830 874 0.014 68.4 35.07 95 C 840 890 0.028 28.6 34.89 94.4 B 830876 0.032 25.6 35.31 94.7 L 825 859 0.035 53.6 36.02 96 R 840 882 0.01465.4 35.07 95.2 4 C 300 450 270 290 0.017 16.5 110 93.1 5 C 300 — 260270 0.017 13.1 116.1 96.3 6 no T 60 450 932 987 0.019 — 31.34 94.4 C 930990 0.017 677 31.30 94.4 B 905 946 0.011 — 32.71 95.7 L 925 971 0.014 —31.86 95.3 R 910 964 0.016 — 32.09 94.4 7 C 60 800 540 580 0.018 2.2953.4 93.1 8 C 300 450 310 313 0.018 13.3 98.8 99 9 C 300 — 250 260 0.02 4.89 119.8 96.2 10 C 60 800 230 240 0.02  11.2 133.5 95.8

[0058]FIG. 7 shows the ET at the amorphous Al₂O₃ layer of 60 Å in Table4, as a function of an applied voltage. That is, reference numerals 710,715, 730 and 735 indicate ET values for the cases No. 1, No. 7, No. 3and No. 6 respectively of Table 4, as a function of applied voltage. Asshown in FIG. 7, if the secondary densification using O₂ is performed at450° C. for 30 min and the primary densification of N₂ is performed at850° C. for 30 min (730 and 735), i.e., in the cases No. 3 and No. 6 ofTable 4, the measured ET values approximate the theoretical ET value of30 Å.

[0059] Referring to FIG. 8, reference numerals 810, 815, 830 and 835indicate leakage current densities for the cases No. 7, No. 1, No. 6 andNo. 3 respectively of Table 4, as a function of applied voltage. Asshown in FIG. 8, among the cases 730 and 735 approximating thetheoretical ET value as illustrated in FIG. 7, i.e., in the cases No. 3and No. 4 of Table 4, case No. 3 exhibits a lower leakage currentdensity at driving voltages of 2 V or less. Thus, if the secondarydensification with O₂ is performed at approximately 450° C. for 30 minaccording to the conditions of case No. 3 of Table 4, i.e., after theRTN process, and the primary densification with N₂ is performed at 850°C. for 30 min, then the electrical characteristics of the capacitor areexcellent.

[0060] The effect of the secondary densification will be described asfollows. The temperature for the secondary densification is set to 450°C., which can produce excellent electrical characteristics of acapacitor as described above. Also, whether the ambient gas for thesecondary densification is a gas other than O₂, (i.e., N₂), or whetherthe secondary densification is performed, are set as variables. The timefor the secondary densification and the thickness of the amorphous Al₂O₃layer are also set as variables. The ET value and the leakage currentdensity are measured as these variables are changed. The conditions areshown in Table 5. TABLE 5 Time for Reference Thickness of Al₂O₃secondary numeral layer (Å) Ambient gas densification (min) 910 40 N₂ 10920 50 O₂ 10 930 50 O₂ 30 940 50 N₂ 10 950 60 O₂ 10 960 60 O₂ 30 970 60N₂ 10 980 60 none  0

[0061]FIG. 9 shows the ET and leakage currents for the variousconditions shown in Table 5. Reference numeral 940 represents the lowestET and the highest leakage current density. However, reference numerals950, 960, 970 and 980, for an amorphous Al₂O₃ layer of approximately 60Å, represent ETs and leakage current densities which are similar to eachother. Also, as the amorphous Al₂O₃ layer is closer to 40 Å (910), theET values are similar and the leakage current density is increased.Thus, in the amorphous Al₂O₃ layer of approximately 60 Å, the propertiesof capacitor change little without regard to whether the secondarydensification is performed or not, to what ambient gas is used, or tochanges in secondary densification time. This means that the secondarydensification is not always a required step. In other words, thesecondary densification is for compensating for the primarydensification. Even through the plate node 500 is formed on thedielectric layer 400 without the secondary densification, a capacitorhaving excellent characteristics can be realized. That is, when theamorphous Al₂O₃ layer and the plate node 500 are formed after an RTNprocess of the storage node 200, and then the primary densificationusing N₂ at approximately 850° C. for 30 min is performed, theelectrical characteristics of the capacitor are excellent.

[0062] Accordingly, the amorphous Al₂O₃ dielectric layer is formed onthe storage node using a method for supplying each reactive vapor phasematerial from several sources on a layer i.e., the storage node, where areaction, e.g., deposition, is performed, in cycles, e.g., ALD method.During forming the amorphous Al₂O₃ layer, the amorphous phase can berealized using the method for supplying reactive vapor phase materialson a layer where a reaction is performed in cycles. Also, by such amethod, no impurity remains in the amorphous Al₂O₃ layer. The amorphousAl₂O₃ layer has a low O₂ diffusivity. Thus, when a conductive layer ofthe silicon group is employed as the storage node, it is possible toprevent the equivalent oxide layer from growing excessively. That is, acapacitor of the SIS structure can be realized, like in the capacitor ofthe ONO structure, to thereby overcome difficulties due to a change ofthe structure of the capacitor to the MIS structure or MIM structure.

[0063] Also, an amorphous Al₂O₃ layer having a smooth morphology andhigh conformity can realize a step coverage of approximately 100%. Thus,the storage node can be formed as a cylinder type, an HSG type or astack type, to thereby increase capacitance. The amorphous Al₂O₃ layerhas a dielectric constant equivalent to that of an aluminum layer of acrystalline phase, to thereby realize high capacitance.

[0064] After forming the plate node on the amorphous Al₂O₃ layer, theamorphous Al₂O₃ layer can be densified by annealing at a temperaturebelow the temperature of crystallizing the Al₂O₃, e.g., at approximately850° C. The densification reduces the thickness of the amorphous Al₂O₃layer and increases the refractivity. That is, the dielectric constantof the amorphous Al₂O₃ layer is increased. Also, the thickness of theequivalent oxide layer is reduced, so that a thickness approximating thetheoretical ET value, e.g., approximately 30 Å, can be realized, tothereby increase capacitance.

What is claimed is:
 1. A capacitor of a semiconductor device,comprising: a storage node; a dielectric layer formed of amorphousAl₂O₃, on the storage node; and a plate node formed on the dielectriclayer.
 2. The capacitor of claim 1, wherein the storage node is apolycrystalline silicon layer doped with an impurity.
 3. The capacitorof claim 1, wherein the storage node has a three dimensional structureselected from the group consisting of a stack type, a hemisphericalgrained silicon layer type and a cylinder type.
 4. The capacitor ofclaim 1, wherein the amorphous Al₂O₃ dielectric layer is formed by amethod of supplying in sequence reactive vapor phase materials on thestorage node.
 5. The capacitor of claim 4, wherein the method ofsupplying in sequence the reactive vapor phase materials on the storagenode is an atomic layered deposition method.
 6. The capacitor of claim1, wherein the thickness of the amorphous Al₂O₃ dielectric layer is10-300 Å.
 7. The capacitor of claim 6, wherein the thickness of theamorphous Al₂O₃ dielectric layer is 40-80 Å.
 8. The capacitor of claim1, wherein a reaction preventing layer is further formed between thestorage node and the amorphous Al₂O₃ dielectric layer.
 9. The capacitorof claim 8, wherein the reaction preventing layer is formed of oneselected from the group consisting of silicon oxide, silicon nitride andsilicon oxynitride layer.
 10. The capacitor of claim 1, wherein theplate node is a conductive layer consisting of one of a refractorymetal, a refractory metal silicide material, a refractory metal nitridematerial and a polycrystalline silicon doped with impurities, in whichthe refractory metal is one selected from the group consisting of W, Mo,Ta, Ti and Cr.
 11. A method for forming a capacitor of a semiconductordevice comprising: (a) forming a storage node; (b) forming a dielectriclayer of amorphous Al₂O₃, on the storage node; and (c) forming a platenode on the dielectric layer.
 12. The method of claim 11, wherein thestorage node is a polycrystalline silicon layer doped with an impurity.13. The method of claim 11, wherein the storage node has athree-dimensional structure selected from the group consisting of astack type, a hemispherical grained silicon layer type and a cylindertype.
 14. The method of claim 11, further comprising forming a reactionpreventing layer on the storage node, before of forming the dielectriclayer.
 15. The method of claim 14, wherein the reaction preventing layeris formed of one selected from the group consisting of silicon oxide,silicon nitride and silicon oxynitride layer.
 16. The method of claim14, wherein the reaction preventing layer is formed by annealing thestorage node at 300-1200° C.
 17. The method of claim 16, wherein theannealing is performed by a rapid thermal process in an ambient N₂source gas.
 18. The method of claim 11, wherein the amorphous Al₂O₃dielectric layer is formed to have a thickness of 10-300 Å.
 19. Themethod of claim 18, wherein the amorphous Al₂O₃ dielectric layer isformed to have a thickness of 40-80 Å.
 20. The method of claim 11,wherein the amorphous Al₂O₃ dielectric layer is formed by supplying insequence reactive vapor phase materials on the storage node.
 21. Themethod of claim 20, wherein supplying in sequence reactive vapor phasematerials on the storage node is performed with an atomic layereddeposition.
 22. The method of claim 21, wherein the atomic layereddeposition is performed using one selected from the group consisting ofAl(CH₃)₃ and AlCl₃ as an aluminum source.
 23. The method of claim 21,wherein the storage node is processed by hydrogen passivation treatmentbefore performing the atomic layered deposition.
 24. The method of claim11, wherein a primary densification is performed on the amorphous Al₂O₃dielectric layer, after forming the plate node.
 25. The method of claim24, wherein the primary densification is performed by annealing theamorphous Al₂O₃ dielectric layer at a temperature below the temperatureof crystallizing the amorphous Al₂O₃ layer.
 26. The method of claim 25,wherein the primary densification is performed at 150-900° C.
 27. Themethod of claim 26, wherein the primary densification is performed at850° C.
 28. The method of claim 25, wherein the annealing is performedusing an ambient gas selected from the group consisting of O₂, NO and N₂gas, or in a vacuum.
 29. The method of claim 24, wherein a secondarydensification is additionally performed on the amorphous Al₂O₃dielectric layer, before forming a plate node.
 30. The method of claim29, wherein the secondary densification is performed by annealing theamorphous Al₂O₃ dielectric layer at a temperature below the temperatureof crystallizing the amorphous Al₂O₃ layer.
 31. The method of claim 30,wherein the secondary densification is performed at 150-900° C.
 32. Themethod of claim 30, wherein the secondary densification is performedusing an ambient gas selected from the group consisting of O₂, NO and N₂gas, or in a vacuum.
 33. The method of claim 11, wherein the plate nodeis a conductive layer consisting of one of a refractory metal, arefractory metal silicide material, a refractory metal nitride materialand a polycrystalline silicon doped with impurities, in which therefractory metal is one selected from the group consisting of W, Mo, Ta,Ti and Cr.